Lots of change out there today, and more to come tomorrow. It's a good time to keep the head up and be aware of changing snow conditions. Cautious terrain choices are recommended. Ice climbers respect terrain traps, dry avalanches are likely.
Weather Forecast
The snow is expected to taper overnight, before another round starts mid day friday. The winds will also decrease, but will remain at the perfect level for slab development. Wind directions will vary locally, but a prevailing SW-S flow will be the main theme. Temperatures will remain similar today. A daytime high of -4 at valley bottom.
Avalanche Summary
Field teams remoted a sz2 from 100m away this afternoon. The terrain was a 40-45 degree unsupported roll with a variable snow pack at the low alpine elevation range. The avalanche involved only the storm snow, the failure plain was the facet layer from the cold snap. A natural sz2 was also visible in an alpine bowl to the west.
Snowpack Summary
At upper treeline elevations we have had 42cm's of snow in the last 48hrs. This new snow has come in two separate storm events. The upper snow pack has a storm weakness (storm shear) that is down about 20cm's (depending on the area). The upper layer is slightly stiffer (due to wind) which will create a short term avalanche problem in itself. A larger concern is the general storm interface down 42cm's. The quality of the bonding within these layers is spotty, and generally suspect. A related concern is in the thinner areas. Lots of whumphing and cracking where the base has no structure or support. The general summary is it is a very touchy upper snowpack sitting a weak facetted base. At lower elevations, the storm snow is less wind effected and generally bonding well to itself, and other layers. \
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.